The ATIC Experiment and Beyond

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The ATIC ExperimentandBeyond

• John P. Wefel
• Louisiana State University
• with the ATIC Collaboration
• July, 2006

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The ATIC Collaboration
J.H. Adams2, H.S. Ahn3, G.L. Bashindzhagyan4,
K.E. Batkov4, J. Chang6,7, M. Christl2, A.R.
Fazely5, O. Ganel3 R.M. Gunasingha5, T.G.
Guzik1, J. Isbert1, K.C. Kim3, E.N. Kouznetsov4,
M.I. Panasyuk4, A.D. Panov4, W.K.H. Schmidt6,
E.S. Seo3, N.V. Sokolskaya4, J. Watts, J.P.
Wefel1, J. Wu3, V.I. Zatsepin4

• Louisiana State University, Baton Rouge, LA, USA
• Marshall Space Flight Center, Huntsville, AL, USA
• University of Maryland, College Park, MD, USA
• Skobeltsyn Institute of Nuclear Physics, Moscow
  State University, Russia
• Southern University, Baton Rouge, LA, USA
• Max Plank Institute für Space Physics, Lindau,
  Germany
• Purple Mountain Observatory, Chinese Academy of
  Sciences, China

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Standard Model of Cosmic Ray Acceleration

• Supernova shock waves may accelerate cosmic rays
  via first order Fermi process
• Model predicts an upper energy limit Emax Z x
  1014 eV
• ? composition growing heavier with increasing
  energy

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Supernovae and Cosmic Rays

• Since 1960s SN associated with CR .why?
• Energetics take energy density in cosmic rays
  and a lifetime of 10-100 million years, to obtain
  the power needed to sustain CR in the galaxy.
  Ask what objects can produce such a power?
• Answer was/is Supernovae explosions

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• Energetics
• CR energy density ? 1eV/cm3
• Residence time in the galaxy ? 2.6x107 yrs
• Power required 2.5X1047 ergs/yr
• A Type II Supernova yields 1053ergs
• Almost all of it goes into neutrinos
• 1051 ergs in the blast wave
• SN rate ? 2/century ? 2X1049ergs/yr
• Blast wave must convert 1 of its energy into
  cosmic rays.
• Diffusive Shock Acceleration required

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Standard picture of cosmic ray acceleration in
expanding supernova shocks
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Exploding Stars

• Novae, Supernovae, Hypernovae/Collapsars .
• Hypernovae/Collapsars may give rise to gamma-ray
  bursts and may involve a black hole.
• Supernovae are explosions of massive stars, say gt
  5 solar masses which lead to neutron star
  (pulsar) or black hole remnants.
• Types I, IA, II, III and variations
• Classified by Radio emission and Optical
  spectra
• Novae are explosions of small stars leading to
  ring nebulae, for example.
• Remnants

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Advanced Thin Ionization Calorimeter
(ATIC)Science Objectives

• Investigate the nature of the cosmic ray
  accelerator
• Look for evidence of more than type of source
• Test diffusive shock acceleration models
• Investigate galactic confinement
• Test leaky box and diffusion models
• Investigate cosmic ray leakage from the Galaxy
• Investigate the role of re-acceleration
• Examine the electron spectrum for evidence of
  nearby cosmic ray sources

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ATIC energy range
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ATIC Instrument Details

• Si-Matrix 4480 pixels each 2 cm x 1.5 cm mounted
  on offset ladders 0.95 m x 1.05 m area 16 bit
  ADC CR-1 ASICs sparsified readout.
• Scintillators 3 x-y layers 2 cm x 1 cm cross
  section Bicron BC-408 Hamamatsu R5611 pmts both
  ends two gain ranges ACE ASIC. S1 336
  channels S2 280 channels S3 192 channels
  First level trigger S1-S3
• Calorimeter 8 layers (10 for ATIC-3) 2.5 cm x
  2.5 cm x 25 cm BGO crystals, 40 per layer, each
  crystal viewed by R5611 pmt three gain ranges
  ACE ASIC 960 channels (1200 for ATIC-3).

Data System All data recorded on-board 70 Gbyte
disk (150 Gbyte for ATIC-3) LOS data rate 330
kbps TDRSS data rate 4 kbps (6 kbps for
ATIC-3) Underflight capability (not
used). Housekeeping Temperature, Pressure,
Voltage, Current, Rates, Software Status, Disk
status Command Capability Power on / off
Trigger type Thresholds Pre-scaler
Housekeeping frequency LOS data rate, Reboot
nodes High Volt settings Data collection on /
off Geometry Factors S1-S3 0.42 m2sr S1-S3-BGO
6 0.24 m2sr S1-S3-BGO 8 0.21 m2sr
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Antarctica

• ATIC is constructed as large as possible and must
  be flown for as long as possible to obtain events
  in the up to 100 TeV energy region.
• Long Duration Ballooning (LDB) from McMurdo
  Station, Antarctica gives the longest possible
  flights.
• So, take ATIC to the frozen continent

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LDB Facilities (new)
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Flight and Recovery
The good ATIC-1 landing on 1/13/01 (left) and the
not so good landing of ATIC-2 on 1/18/03 (right)
Launch of ATIC-2 in Dec. 2002
ATIC is designed to be disassembled in the field
and recovered with Twin Otters. Two recovery
flights are necessary to return all the ATIC
components. Pictures show 1st recovery flight of
ATIC-1
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All Particle Spectrum
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Charge resolution in the p-He group
EBGO gt 50 GeV
EBGO gt 500 GeV
EBGO gt 5 TeV
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Deconvolution
Primary Energy Spectra (E0)
Instrument Response
Measured Energy Deposit Spectra (Ed)


(must solve the inverse problem)
A(E0,Ed) response matrix
Obtained from FLUKA model of instrument
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Cosmic Ray Propagation
Leaky Box Model
where
from HEAO-3-C2
for R gt 4.4 GV
with ? 2.23 for Z gt 2
But,
at high energy leads to conflict with anisotropy
measurements
And,
Some weak re-acceleration in turbulent magnetic
fields seems likely
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Cosmic Ray Propagation
Diffusion Model
Osborne and Ptuskin (1988) proposed
where R0 5.5 GV
?
Spectral index 2.6 at high energy
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Electrons ( negatrons positrons )

• Electrons are both Primary (source produced) and
  secondary (produced by interactions in ISM
• Electrons are accelerated in Supernovae Remnants
  (SNR)
• Electrons lose energy by Synchrotron Radiation,
  Compton collisions and Bremstrahlung
• Electron Energy Loss proportional to E2
• Protons, in comparison, lose E proportional to
  log E
• Thus, at very high Energy, electrons do not last
  a long time
• Cannot get here from very far away (local
  source)
• Source (accelerator) must be relatively young
• High energy (TeV) electrons may show nearby SN
  source(s)

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ATIC can Measure High Energy Electrons
Typical (p,e,?) Shower image in ATIC (from Flight
data) 3 events, energy deposit in BGO is about
250 GeV Electron and gamma-ray showers are
narrower than the proton shower Gamma-ray shower
No signals in the top detectors around the shower
axis
electron
gamma
Proton
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Shower width (r.m.s. ) distribution of protons
and electrons in BGO2
Solid line from 150 GeV electrons, Dashed line
from protons with comparable energy deposit in
the BGO block
Simulation
CERN calibration
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F (E10/Sum)(r.m.s.)2 distribution in
BGO10 Solid line is from 150 GeV
electrons Dashed line is from protons with
comparable E deposit in BGO
Simulation
CERN
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• Background Level (inferred from the CERN
  beam test)
• 8741 proton events with energy deposit
  comparable to that of the electron events Only 3
  protons mimic electrons for a cut at 80 of the
  electrons.
• A proton deposits on average about 40 of its
  energy in ATIC
• Rejection power 8741/32.51.7 13000 (for
  a proton spectral index of 2.7)

Expected Balloon Observation
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Single charge good geo. gt50GeV
After step 1
The method to select electron events 1.
Rebuild the shower image, get the shower axis,
and get the charge from the Si-detector
(?2lt1.5) 2. Shower axis analysis In Carbon to
reject ? and Proton (its first interaction point
is not in carbon) 3. Shower width analysis in
BGO1 and BGO2 4. Shower F value analysis in BGO7
and BGO8
After step 2
After step 2
After step 3 4
After step 3 4
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Comparing with electron models
Absolute electron spectrum spectrum comparison
with calculated model by a diffusion coefficient
of D2.0X1029(E/TeV)0.3cm2s-1 and a power index
of injection spectrum 2.4 T. Kobayashi, et al.
Astrophys. J. 601 , 340 (2004)
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Summary

• ATIC is providing new data in an unmeasured
  region of the spectrum and is finding new
  features
• Not pure power law spectra
• H and He are different (why?)
• Galactic transport changes in this region leading
  to spectral changes with energy
• Multiple source models will, almost assuredly, be
  required (Exploding Stars of different types
  ? )
• ATIC has the most significant measurement of the
  high energy electron spectrum
• Feature in the spectrum at 300-500 GeV
• Evidence for nearby Supernovae source ?
• Evidence for Dark Matter annhilation ?
• No evidence for trans-TeV electron flux

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And Beyond

• Balloon Missions
• Re-flights Cream, Tracer (just completed), ATIC
  (?)
• CREST for TeV electrons
• Space Missions
• PAMELLA (recently launched)
• ISS AMS (?), CALET (?), others
• Free-flyers GLAST (next year)
• Plans in Russia (?)

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And Beyond .

• Ground-based
• Air Shower Experiments
• Air Cherenkov Telescopes

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Motivation for KASCADE-Grande

• energy spectrum and composition 1016eV-1018eV
• iron knee ?
• origin of the knee ?
• galactic to extragalactic transition?
• Testing hadronic interaction models
• Anisotropies

?
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And Beyond

• High Energy Astrophysics from / on
• The Moon (? ? ?)
• Whatever happens
• The future will be interesting !

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Current and Recent Balloon Instrumentsto measure
high energy (gt 1 TeV) cosmic ray composition

• JACEE
• Series of emulsion experiments, 1979 1994
• 11 balloon flights, cumulative exposure 644 m2
  hrs _at_ 3.5 5.5 g/cm2
• Zenith angle acceptance out to tan ? 72-79 ?
  80 m2 sr days exposure
• Highest energy proton event 800 TeV
• RUNJOB
• Series of emulsion experiments, 1995 1999
• 10 balloon flights, cumulative exposure 575 m2
  hrs _at_ 9.0 10.7 g/cm2
• Highest energy proton event seen at E gt 1 PeV
• ATIC
• Silicon matrix-scintillator-BGO calorimeter
• 2 balloon flights, 2000-2003, 31 days exposure
• ? 7 m2 sr days exposure
• 3rd LDB Antarctic flight scheduled for
  December 2005 -- BUT
• CREAM
• Combined Scintillator, Si Charge Detector,
  W-scintillator calorimeter, TRD
• One balloon flight, 2004-2005, 41 days
• ? 12 m2 sr days exposure

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• TRACER
• Scintillator-Cherenkov-TRD for 8 Z 26
• Two flights, 1999-2004
• ? 40 m2 sr days exposure
• TIGER
• Scintillator-Cherenkov-fiber hodoscope to
  measure Z 30
• Three flights, 1997-2004, 50 days exposure
• ? 4 m2 sr days exposure
• Originally planned as first ULDB instrument
  future flights planned
• CAKE
• Nuclear track detectors (CR-39, Lexan) to
  measure 6 Z 74
• One flight, 1999, 22 hours exposure
• ? 0.9 1.8 m2 sr days exposure _at_ 3 3.5
  g/cm2
• Planning to fly larger version on ULDB

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All particle spectrum ATIC, emulsion, and EAS
data
RUNJOB
JACEE
CASA-BLANCA
Tibet
KASKADE
TUNKA
ATIC-2